PHOTO COURTESY OF NASA/JPL
An enhanced false color image shows the asteroid Ida with its satellite Dactyl to the right. Researchers believe they can determine the age of any asteroid from its surface colors.

Colors reveal ages
of asteroids

A team led by a UH astronomer
sees the effects of weathering

Asteroids change color as they age because of space weathering effects, a team led by University of Hawaii astronomer Robert Jedicke has discovered.

The findings, reported in yesterday's issue of the journal Nature, are based on color measurements of more than 100,000 asteroids.

"There is a clear range and distribution of the colors of the asteroids," said Jedicke. "We detected the relationship by looking at the color of an asteroid as a function of its age."

Researchers believe they will be able to determine the age of any asteroid from its surface color, as they obtain colors of the youngest known asteroid surfaces.

David Nesvorny of the Southwest Research Institute in Boulder, Colo., estimated asteroid ages from 6 million to 3 billion years.

"The mystery is that ordinary ... meteorites have a bluish color relative to the reddish color of the asteroids from which they were supposedly released," Nesvorny said.

Jedicke said asteroids of different colors and the fact that space weathering takes place have been known for a long time. But the connection between ages and colors of asteroids and weathering effects is new.

"Asteroids get more red with time in exactly the right manner and at the right rate to explain the mystery of the color difference between them and ordinary ... meteorites," he said.

"If you were given a piece of rock from the Grand Canyon," he said, "you might expect that it would be red, like the color pictures in travel magazines. You'd be forgiven for questioning its origin if the rock had a bluish color.

"But if you were then told that the rocks turn from blue to Grand Canyon red because of the effects of weather, then everything might make sense. Your gift is simply a fresh piece of exposed rock, whereas the pictures you've seen show weathered cliff faces millions of years old."